Rivet Clip is an interesting, albeit more "dangerous" solution for adding your own slim belt clip to a plastic case. NOT recommended for attaching to leather.

The Sena Leatherskin or flip cases are awesome, and they have attachable plastic belt clips.

Waterfield Designs (sfbags.com) features a really, really durable pouch that can have a belt clip — also can have a mini pouch to hold your earphones, if they're small enough

iSkin features some really cool designs with a rather large, but flexible belt clip. Unfortunately their build quality really wasn't up to par last time I tried them out. Case broke in about a week.

I've never tried Speck cases, but they do have some with belt clips.

Good hunting! Let us know if you find another one that's worth a look!

yeah, it's a gorgeous case — and so is the one you linked to in your comment. I'll definitely try to check it out. I like how it has a Lanyard!